South of the border, down Mexico way, a new and savage revolution rages just beyond our inspection lanes. After less than five years of fighting, estimates of the dead have reached 22,000.

The rate of killing accelerates each month. And Washington covers its eyes like a kid at a scary movie. Well, the Mexican narco-insurgency, in which well-armed guerrilla forces confront the authority and presence of the state, is our No. 1 security challenge.

The chaos in northern Mexico has far deeper implications for our country than Islamist terror or even an Iranian nuclear capability (as grim as those threats are).

The rule of law has collapsed from Tijuana on the Pacific’s edge to Matamoros and the Gulf of Mexico. Major cities are now “ungoverned spaces,” as our diplomats refer tidily to distant trouble spots.

More people now die violently on our southern border than in Somalia, Yemen or even Afghanistan. But Washington doesn’t know what to do about Mexico. So Washington does nothing much.

Our ruling class simply doesn’t feel the pain. So the DC elite demonizes Arizona’s desperate effort to shove the narco-revolution’s disorder back across the border. Murdered ranchers, overwhelmed emergency rooms and soaring crime rates in our border states mean less to the White House than a terrorist detainee’s claims of abuse. Our governing elite pretends that illegal immigration, torrential crime where illegals cluster, overcrowded prisons, Mexico’s narco-insurgency, legal cross-border commerce and the drug trade are separate issues, to be addressed discreetly.

But these issues are all interwoven with the Mexican government’s existential crisis. Drug wealth fuels criminal empires. Those narco-empires are now so powerful that they’ve risen against the state. Human trafficking is a useful sideline for drug lords. And illegal immigration drives crime rates in bankruptcy-threatened US cities and states.

Cross-border trade’s the next target. Narco-insurgents now feel sufficiently confident to attack Mexican army installations and US consulates. The maquiladoras, those thousands of assembly plants along the border, won’t escape the mayhem. Given their enormous contribution to Mexico’s fiscal stability and employment rates, those plants are obvious targets as the narco-challenge to the state intensifies.

Mexican journalists, too, have been killed by the hundreds. Their torture and execution doesn’t generate much excitement north of the border, though. It’s their bad luck to be butchered by Mexican narcos. Had they been killed accidentally by US forces in Iraq or Afghanistan, they’d be famous martyrs.

And Arizona’s “discriminatory” new state law empowering police to pursue criminal aliens? Should Phoenix let the rule of law collapse because Washington prefers political correctness to public safety? In DC, it’s about politics. In Arizona, it’s about survival.

It bewilders me that my fellow citizens don’t take the disintegration of government authority in northern Mexico seriously. As I’ve written repeatedly, no country is more important to us socially, economically and security-wise than Mexico. Afghanistan’s fluff by comparison.

Precisely 100 years ago, in 1910, the Mexican Revolution erupted in northern Mexico — already the most prosperous and industrially developed portion of the country. That revolution lasted a bloody, destructive decade.

It wasn’t the bandido affair beloved of Hollywood knuckleheads, but a complex contest for power with large armies, strategic campaigns, major battles, trench warfare, barbed wire and machine guns. In 1915, the military vision of the self-taught Gen. Alvaro Obregon — destined to become Mexico’s president — was more sophisticated than that of the US Army. Mexico pioneered the 20th century’s revolutions.

Since then, northern Mexico — from the border cities southward through the industrial powerhouse of Monterrey — has continued to be the country’s primary agent of change. Influenced by its proximity to America, the north long has been a different country from the impoverished states south of the capital.

Now a new Mexican revolution is underway in the vital north. In 1910, idealists struggled to change an autocratic regime. In 2010, criminal syndicates fight to wrest power from a democratic government and to grab market share from each other.

(In an eerie parallel, a bloody strike in the northern mining center of Cananea helped ignite the 1910 revolution; today, a three-year-long strike in Cananea by mining and metal workers signals a new generation’s impatience with the status quo — and we’re just not paying attention.)

During that earlier revolution, the citizens of El Paso, Texas, and Douglas, Arizona, gathered to watch the battles just across the border as Pancho Villa’s troops drove out the Federals, then as the Constitutionalists defeated Villa. Those spectators were confident in their immunity as American citizens.